Paris and London — Four months ago, in the aftermath of the deadly Paris attacks, there was widespread agreement among European leaders that the continent’s intelligence agencies needed to share more information to prevent radicals’ future attacks.

Today, the disconnect between intelligence agencies is still gaping. According to Turkish President Recep Tayyip Erdoğan, Turkish authorities deported Brussels attack suspect Ibrahim el-Bakraoui to the Netherlands last summer – and warned Belgium of his terrorist ties. Yet Bakraoui, a Belgian national, was released without charge. He is believed to have been a suicide bomber in Tuesday's attacks in Brussels which left more than 30 people dead and hundreds injured.

The inability of Europe's security agencies to cooperate on terrorism reveals just how difficult it is proving to overcome international jealousy over intelligence, despite shared interests. Unlike a common energy policy, or even a common currency, sharing intelligence or defense capabilities cuts to the heart of national sovereignty.

Alain Bauer, a French criminologist who has advised several French governments on counterterrorism, says that authorities need to overcome their possessiveness of their intelligence, putting the focus solely on terrorism and not the entire body of information a nation accumulates.

Counterespionage, or activities designed to prevent or thwart spying by an enemy, "is an absolute secret that you don’t even tell your wife about, let alone other agencies. If counterterrorism is treated as counterespionage, there will be no sharing,” he says. “The problem is that we don’t have enough counterterrorism, which unlike counterespionage is short-term and can easily be shared.”

Underused tools

Europe has already been moving in that direction but not fast enough, say experts. In January, Europol – Europe’s closest version to a bloc-wide police corps – launched a special unit, the European Counter Terrorism Center, where some 50 specialists will collect and evaluate information about suspected terrorists.

At the time the Hague-based center issued a threat assessment of Islamic State, based on the investigations of the Nov. 13 attack in Paris that took 130 lives. “Intelligence suggests that IS has developed an external action command trained for special forces-style attacks in the international environment,” it concluded.

Still, Dimitris Avramopoulos, the EU commissioner for Migration, Home Affairs, and Citizenship, said the unit is not being vigorously used by European nations.

Europeans also created the Counter-Terrorism Group (CTG), a network of European intelligence agencies, but it operates on a voluntary, need-to-know basis. Last month, the CTG announced that it would form a platform for counterterrorism sharing between its 30 members, which include the EU’s 28 member states as well as Norway and Switzerland. The platform, which is to be launched during the first half of this year, was formed with the goal of preventing Paris-style attacks.

Sajjan Gohel, the London-based international security director for the Asia-Pacific Foundation, says cooperation has increased since the Paris attack, leading to dozens of raids and ultimately last Friday's arrest of Salah Abdeslam, the last suspect from Paris believed to be alive. But "for every individual arrested, captured, prosecuted, there are potentially at least another five coming along the assembly line. It never actually ends,” he says.

'We cannot keep learning the hard way'

For many there are clear security failures at play too. It is unclear whether the attacks in Brussels could have been prevented with more coordination between agencies, but Turkish President Erdoğan's claim – that Bakraoui was deported and flagged as a foreign fighter – puts European intelligence under a harsh spotlight.

It’s not clear what the Dutch and Belgian governments did with the intelligence on Bakraoui, who authorities say was among the suicide bombers at Zaventem Airport. Still, many officials say that a lack of information-sharing points to an overall European weakness.

“We cannot keep learning the hard way, but the events in Brussels show, once again, that we absolutely need more coordination and more information exchange,” said Mr. Avramopoulos. “The fact that the perpetrators of the Paris and Brussels attacks were known to the police proves this once again. Information gathering and information exchange are the cornerstone of our security. Our information needs to be inter-connected. Our systems need to talk to each other.”

EU interior ministers are meeting today in an emergency session – as they did after the attack in Paris – and will renew their calls for more robust use of EU databases and for new instruments like the Passenger Name Record to track air passengers in and out of the EU. It has yet to be implemented.

Christina Schori Liang, program adviser in the Emerging Security Challenges Program at the Geneva Centre for Security Policy, says such inability to cooperate is creating a gap which terrorists profit from. “There is a blindness of the threat,” she says. “Here we are, Islamic State is expanding terror into the heart of Europe, and there is still an unwillingness to cooperate effectively across borders.”

Lessons from Britain?

Belgian Prime Minister Charles Michel reiterated his call for a European domestic intelligence service in the wake of the Paris attack, when the investigative trail led authorities to Brussels. But there is little appetite for such a cross-border agency.

First, sharing opens up possibilities to leaks, says Colin Clarke, a terrorism researcher at RAND. “This is an issue both across Europe, between Germans and French, Brits and Italians, but also within individual countries,” he says.

And systems are only as strong as their weakest link.

Many look to Britain as an example of how to evolve and respond to the terrorist threat. Paul Lashmar, a senior lecturer in journalism at the University of Sussex and former investigative journalist focusing on intelligence agencies, says that since 9/11, MI5 and its foreign intelligence sister MI6, the signals intelligence agency GCHQ, and police forces are working together to create a full picture of the threat facing the UK. “MI6 picks up information, MI5 looks at it locally with the police, and GCHQ feeds in SIGINT [signals intelligence].”

“The security services are highly fragmented along linguistic lines, with some forces speaking French, some German, and some Flemish. And there are very few Arabic speakers on the forces,” says Mr. Clarke.